The Opening (開門の日 Kaimon no Hi?) is an event in Tales of Berseria. It was since this day that people began to see daemons.
History
Ten years prior to the events of the story, brigands attacked Aball for reasons unknown on a Scarlet Night. The brigands' malevolence resulted in them becoming daemons and attacking the village, while chasing Celica Crowe into the shrine in Tranquil Woods. Artorius Collbrande rushed after her, slaying the daemons until he made his way to her. When a daemon was about to attack him with his back turned, Celica pushed him away and received the blow that forced her into the depths of the shrine as a mouth of a mysterious entity devoured her. Artorius was in pain after losing his beloved, and Melchior then appeared, explaining that Aball's inhabitants offered him and his family to the daemon brigands, explaining that the "reason" upon which they acted was so they could escape and hide.
A bright light emerged from the shrine's depth, surprising Artorius, who noted that it must have been in this place that the Empyrean they were looking for was located. Celica and her unborn baby were then reborn as malakhim, and Artorius forged a pact with Celica's malak reincarnation, Seres. Angry at people's selfishness, Artorius declared in that moment to put an end to the world's suffering with Melchior's help, intending to resurrect Innominat and use him to strip emotions from people, which would result in a lack of malevolence, therefore eliminating the threat of daemons. While Celica had no resonance, her unborn child did, and this resulted in Innominat's resurrection being half-complete, thereby triggering humans' inner resonance and enabling them to see daemons, as well as suppressing most of malakhim's free will.